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#300
by
psloss
on 23 Jan, 2006 11:53
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I won't forget these questions...I've had 'em for 10 years or more; I just have to figure out how to communicate them better. I'll hope that these great ops folks from NASA and the contractors will stick around the site and I'll ask later. Maybe it's just me, but I do also see this thread serving as a running FAQ thread.
Philip Sloss
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#301
by
Rocket Nut
on 23 Jan, 2006 12:21
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psloss - 23/1/2006 7:53 AM
Maybe it's just me, but I do also see this thread serving as a running FAQ thread.
Philip Sloss
I can certainly agree with that statement...so keep on Asking your Questions...Frequently...
Cheers,
Larry
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#302
by
Chris Bergin
on 23 Jan, 2006 14:29
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I agree. I also want to avoid splitting this thread (I know it's a long thread) given it's a fantastic resource by way of FAQ. I think there's a lot of us that wished we had something like this in the 80s and 90s.
As the site matures I'm sure they'll be some level of expansion in the forum layout - and this sort of thread will remain intact for as long as this site remains live.
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#303
by
Polecat
on 24 Jan, 2006 05:33
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Hello.
What makes the SSMEs gimbal? Is it hydrolic? I wondered about this as I believe it would be a lot of force to move the bells when they are firing!
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#304
by
Chris Bergin
on 24 Jan, 2006 09:10
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Polecat - 24/1/2006 6:33 AM
Hello.
What makes the SSMEs gimbal? Is it hydrolic? I wondered about this as I believe it would be a lot of force to move the bells when they are firing!
On the NASA reference pages it explains this as:
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-mps.html"Three orbiter hydraulic systems provide hydraulic pressure to position the SSME servoactuators for thrust vector control during the ascent phase of the mission in addition to performing other functions in the main propulsion system. The three orbiter auxiliary power units provide mechanical shaft power through a gear train to drive the hydraulic pumps that provide hydraulic pressure to their respective hydraulic systems.
The ascent thrust vector control units receive commands from the orbiter GPCs and send commands to the engine gimbal actuators. The units are electronics packages (four in all) mounted in the orbiter's aft fuselage avionics bays. Hydraulic isolation commands are directed to engine gimbal actuators that indicate faulty servovalve position. In conjunction with this, a servovalve isolation signal is transmitted to the computers.
The SSME hydraulic servoactuators are used to gimbal the main engine. There are two actuators per engine, one for pitch motion and one for yaw motion. They convert electrical commands received from the orbiter GPCs and position servovalves, which direct hydraulic pressure to a piston that converts the pressure into a mechanical force that is used to gimbal the SSMEs. The hydraulic pressure status of each servovalve is transmitted to the ATVC units."
And people wonder why there's a need for a Q and A thread when NASA.gov explains it ever so clearly
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#305
by
mkirk
on 24 Jan, 2006 23:23
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For those of you who like excessive technical detail, here is a link that NASA PAO has seemingly forgotten since they no longer link to it from their mission pages. This is a link to part of the space shuttle crew ops manual (flight manual)...the shuttle version of the Air Force dash one...or NATOPS for any of you Navy Pukes...errr...NAVY people;) Actually it is just Section 2 of the manual (from the 1999 time frame) which describes the orbiter's systems. In many cases it does so in the same manner as the STS News Reference (1988) except that it it much more up to date...newer APUs, IMUs, GPCs etc. This is not the current version of the manual but it is still pretty acurate. The shuttle has gone to a "Glass Cockpit" which really isn't covered in this version but for the most part all that we did with the glass cockpit displays is digitize the old "steam gauges". Most of the CRT displays are still the same and the system's operation is still the same.
For example if you want to see the Launch and Ascent Trajectory Displays (which are actually pretty primitive since they were designed in the 1970's) you will be able to find them in the back of the Guidance, Navigation, and Control (GNC) section.
Main Engine Gimbaling would be in the MPS...sorry but it doesn't explain it any better than what Chris quoted earlier.
http://www.shuttlepresskit.com/STS-105/scom.htmI hope you find it useful!
Mark
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#306
by
jschaef5
on 25 Jan, 2006 01:12
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Alright I got a question regarding the 90 days, or is it 60 days where the next shuttle must be able to take off for a 'rescue' mission incase something goes wrong in space with the first shuttle.
Now I remember seeing a picture with 2 shuttles on 2 seperate pads at once. Why can't they make it a 0 day rule: launch with another shuttle ready to go. That way they won't have to spend time getting the shuttle ready and all that stuff. It just seems safer incase say the shuttle runs into the ISS and takes a huge chunk out and they can only survive on what they have in the shuttle or something. Theres tons of scenarios where they could need rescue in before 60 days is up. I am just wondering why do they say 60 (or 90) and not just go with the safest choice and say 0. I'd guess that 60 would be if they can dock with ISS and foam hit the shuttle and they need a ride home but 60 days isn't much, why not just have it ready at liftoff.
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#307
by
Chris Bergin
on 25 Jan, 2006 14:22
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Welcome to the site - pretty good question...bumped to ensure it's answered.
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#308
by
possum
on 25 Jan, 2006 16:25
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jschaef5 - 24/1/2006 8:12 PM
Now I remember seeing a picture with 2 shuttles on 2 seperate pads at once. Why can't they make it a 0 day rule: launch with another shuttle ready to go. That way they won't have to spend time getting the shuttle ready and all that stuff.
I'm not the expert in this area, but that's never stopped me before so here's my opinion. To have 2 Shuttles ready to go at the same time would be very difficult with only three Orbiters in the inventory. Typically, the Shuttles are all at different stages of preparation; when one is at the Pad being readied for launch, another is being stacked in the VAB, another is in the middle of processing in the OPF, and another has just returned and is beginning processing in the OPF. That was when we had four, and even then, one was usually in an extended maintenance period undergoing upgrades and refurbishment. The 3 remaining Shuttles have seen their last extended maintenance periods (called OMDP, or Orbiter Maintenance Down Period), so that is no longer an issue. However, in order to do what you are proposing we would have to have 2 Shuttles processed and stacked and at the Pad ready to go. That would require us to wait longer and spend more resources (which are getting more scarce each passing day) to get 2 vehicles ready to fly. I believe there are also changes in the configuration of the Orbiter, particularly in the payload bay, depending on the type of mission and payload being flown. So until we know the type and nature of the mission, we can only process the Shuttle up to a certain point. As it stands now, the mission after STS-121 will be prepared to fly the P3/P4 truss combo to ISS. So there is a limit to how far in the process we could go and still be able to reconfigure for a rescue mission, especially since we would not know what we would need for the rescue mission depending on the nature of the emergency. To modify the processing scenario radically in order to muster a rapid response to an emergency would put the rescue mission at a much higher risk. So the 60 days allows us to prepare up to a point of divergence without deviating from our accepted methods and still be able to change the nature of the mission for a rescue using accepted practices and get the next launch off as soon as is deemed safe. If a rescue is not required, the processing would continue as needed to conduct the next mission in the ISS assembly sequence. Hope this helps.
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#309
by
Shuttle Scapegoat
on 27 Jan, 2006 01:26
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The OMSS boom has sensistive imagary devices, Satellites have very sensistive parts, and I'm sure there are other areas, but I've never known how sensistive equirement isn't damaged by the force of a launch. How protected is the Cargo Bay from such forces?
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#310
by
mkirk
on 27 Jan, 2006 02:24
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Shuttle Scapegoat - 26/1/2006 8:26 PM
The OMSS boom has sensistive imagary devices, Satellites have very sensistive parts, and I'm sure there are other areas, but I've never known how sensistive equirement isn't damaged by the force of a launch. How protected is the Cargo Bay from such forces?
I guess I'll take this one-
Anything that is placed in the payload bay has to meet some pretty stringent criteria in terms of safety and structural integrity. You don't want anything to come loose and damage critical orbiter systems and you don't wan't to damage the payload(s) itself. This means that whatever is back there has to be compatible with the payload bay's mounting devices/carriers and has to be built strong enough to deal with the low frequency vibrations and G-forces experienced during launch, on orbit maneuvering, as well as entry and landing. While these are pretty significant on the shuttle it is a much more benign environment than most unmanned vehicles. The shuttle does not normally exceed 3 Gs. The mounting devices are pretty well understood from an engineering perspective which means that payload designers know exactly what kind of flight environment they are designing for.
So while the intstrumentation may be sensitive it is still built rugged enough to satisfy these demands. Payloads are only allowed to draw certain amounts of power from the orbiter...if they have there own systems for power or propulsion, then they must be designed in such a way as to prevent leaks or contamination. Payloads usually have protective thermal blankets as well as covers for sensitive lenses and so on...
Another factor that protects sensitive equipment is that the payload bay is essentially a clean room environment...this is why you see pictures of people working back there with "bunny suits on". The atmosphere is controlled prior to launch to protect against contamination during fueling as well as from the outside environment. For instance at the Launch Pad you want to maintain a positive atmospheric pressure so that the outside sea-side salt air can not enter the payload bay and cause damage to sensitive systems.
I hope that sort of answers your question.
Mark
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#311
by
FransonUK
on 28 Jan, 2006 11:16
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What are the Orbiters primarily made of? Steel?
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#312
by
Stardust9906
on 28 Jan, 2006 11:26
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FransonUK - 28/1/2006 12:16 PM
What are the Orbiters primarily made of? Steel?
The airframe is made of Aluminium.
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#313
by
nacnud
on 28 Jan, 2006 12:44
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Does anyone know anything more about this study,
Shuttle II (Langley 1988), from astronuatix:
In May 1988 NASA Langley studied a new-technologyapproach to improving the shuttle's payload capability. The designwould allow 9,000 to 18,000 kg of additional payload to be carried inan external payload container or in the orbiter.
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#314
by
nacnud
on 28 Jan, 2006 13:47
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Wow, that is very different to what I expected, thanks.
It kind of reminds me of boeing SLI concept pictured below, missing from the picuter is the booster stage which is identical but without the payload canister.
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#315
by
Ben E
on 28 Jan, 2006 15:52
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Sorry, but can I return to jschaef5's question about two Shuttles on the pad at the same time...by asking another question?
Some posters have commented that, when four Shuttles were operational, they were at different stages of processing, it would have been "very difficult" to launch in close proximity to one another. However, there are many examples of missions that were planned to be flown within a couple of weeks of each other - and I'm not just talking about the 'gung-ho', strap-it-on-and-go days of pre-51L.
Back in late 1995, STS-74 lifted-off barely three weeks after STS-73, and only a WEEK after the latter had touched down. Admittedly, STS-73 had been delayed by several weeks itself, which brought the two missions closer together, but this is one of many examples which show it to be technically feasible. Other examples:
* STS-35 lifted-off 17 days after STS-38 in November/December 1990
* STS-39 lifted-off 23 days after STS-37 in April 1991
* STS-55 lifted-off 18 days after STS-56 in April 1993
* STS-68 lifted-off 21 days after STS-64 in September 1994 - and was then followed by ANOTHER launch (STS-66) just 34 days after that.
* STS-70 lifted-off 16 days after STS-71 in June-July 1995.
Each of the above missions featured different orbiters, supposedly at different stages of different processing flows, and yet these short gaps between missions WERE achieved. In the case of STS-64, STS-68 and STS-66, THREE missions - using three separate orbiters - were launched in the space of 55 days.
I do not understand, therefore, how with this breadth of experience of launching orbiters in very close proximity to one another - and even bearing in mind all the lighting constraints needed to view the launch adequately - NASA is now unable to do it again.
Any comments would be appreciated.
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#316
by
psloss
on 28 Jan, 2006 16:39
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Ben E - 28/1/2006 11:52 AM
Back in late 1995, STS-74 lifted-off barely three weeks after STS-73, and only a WEEK after the latter had touched down. Admittedly, STS-73 had been delayed by several weeks itself, which brought the two missions closer together, but this is one of many examples which show it to be technically feasible. Other examples:
* STS-35 lifted-off 17 days after STS-38 in November/December 1990
* STS-39 lifted-off 23 days after STS-37 in April 1991
* STS-55 lifted-off 18 days after STS-56 in April 1993
* STS-68 lifted-off 21 days after STS-64 in September 1994 - and was then followed by ANOTHER launch (STS-66) just 34 days after that.
* STS-70 lifted-off 16 days after STS-71 in June-July 1995.
In each of those cases, the cited launches experienced the several week delay you mention and all were rolled off the pad (with the exception of STS-55), so I think the idea basically comes back to getting a shuttle ready and then setting it aside (so to speak). That's essentially what happened in all of those cases.
STS-35 was shuffled back and forth not just from Pad A to Pad B, but between the VAB and the pads and Columbia between the OPF and VAB. That was "the summer of the hydrogen leak."
STS-39 was rolled back due to ET umbilical door hardware.
STS-55 and STS-68 had main engine shutdowns on the pad.
The STS-70 external tank was attacked by northern flicker woodpeckers.
This is kind of the same "what-if" logistical question I had about having another shuttle ready to do a rescue mission without the CSCS capability that the space station provides. It seems to me that one or the other shuttle would have a decently long "dwell" period, either on the pad or in the VAB, in order to make this possible.
There could also be programmatic issues at present with flying two missions close together -- for example, will there be enough time for the program to thoroughly review all the STS-121 test flight/engineering data for a launch at the end of the May window (which would end in early June) AND still take advantage of the July window for STS-115?
Philip Sloss
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#317
by
STS-Chris
on 28 Jan, 2006 20:45
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Hello, I'm new here, but I'm watching Shuttle missions since STS-99 in 2000.
I saw here that Endeavour is scheduled to fly STS-116, Atlantis STS-117, Endeavour again (STS-118) and then Discovery (STS-119). Is that orbiter flight sequence sure, if STS-121 and 115 are successful?
Are there certain reasons for choosing this orbiter sequence?
Thanks for your answer!
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#318
by
Ben E
on 28 Jan, 2006 23:02
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STS-Chris,
As far as I'm aware, Discovery will fly STS-121 in May 2006 and her next flight will be STS-119 in May 2007. The reason, I believe, is that she is being outfitted to support the new, long-duration power system that utilises the ISS solar arrays. Hence Atlantis and Endeavour will alternately fly the other missions (STS-115 through 118).
No more Orbiter Maintenance Down Periods, though, so after STS-119 the orbiters will pretty much fly in sequence, with Atlantis retiring in 2008 and Discovery and Endeavour flying until the very end.
Thanks for your comments, by the way, Philip. That clarified some of the issues for me - but it does beg one more question. Even setting aside the missions that I cited, which were delayed due to main engine shutdowns etc, I do remember that pre-51L missions COULD be launched at intervals much shorter than the 4-6 month processing flows needed by orbiters today. In 1985, for instance, Challenger and Discovery averaged 2-month turnarounds. Was NASA just cutting corners in their processing flows which it opted not to do in the wake of 51L? Or could such short turnarounds still be possible today?
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#319
by
Chris Bergin
on 29 Jan, 2006 09:50
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Ben E - 29/1/2006 12:02 AM
STS-Chris,
As far as I'm aware, Discovery will fly STS-121 in May 2006 and her next flight will be STS-119 in May 2007. The reason, I believe, is that she is being outfitted to support the new, long-duration power system that utilises the ISS solar arrays. Hence Atlantis and Endeavour will alternately fly the other missions (STS-115 through 118).
No more Orbiter Maintenance Down Periods, though, so after STS-119 the orbiters will pretty much fly in sequence, with Atlantis retiring in 2008 and Discovery and Endeavour flying until the very end.
Thanks for your comments, by the way, Philip. That clarified some of the issues for me - but it does beg one more question. Even setting aside the missions that I cited, which were delayed due to main engine shutdowns etc, I do remember that pre-51L missions COULD be launched at intervals much shorter than the 4-6 month processing flows needed by orbiters today. In 1985, for instance, Challenger and Discovery averaged 2-month turnarounds. Was NASA just cutting corners in their processing flows which it opted not to do in the wake of 51L? Or could such short turnarounds still be possible today?
Well Griffin reckons the 4.5 missions per year with three Orbiters is possible, so it's not vastly different with the turnarounds of old.
